Induction of Growth Promotion and Stress Tolerance in Arabidopsis and Tomato by Plant Growth-Promoting Rhizobacteria
Type of DegreeDissertation
Entomology and Plant Pathology
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Plant growth-promoting rhizobacteria (PGPR) were evaluated for induction of growth promotion in Arabidopsis and enhancement of stress tolerance in tomato under greenhouse and field conditions. Bacillus strain GB03 not only resulted in larger plant size, but significantly enhanced Arabidopsis growth rate and shortened the time to attain each growth stage from the three-leaf stage to inflorescence emergence. Elicitation of Arabidopsis growth promotion by PGPR is most effective during early stages of development. However, induced systemic resistance by PGPR may vary according to plant species and PGPR strain. The interaction between PGPR strain and Arabidopsis root morphology was conducted in a Petri dish system. Bacillus PGPR strains reduced Arabidopsis total root length but enhanced root hair length in a dose-dependent manner. The mechanism of bacilli elicitation of growth promotion may involve the enhancement of root hair development and therefore increase nutrient and water uptake. Tomato was used to study the effect of PGPR on plant growth under different environmental stresses. The effect of PGPR on tomato growth under salt stress was conducted under greenhouse conditions. Some Bacillus PGPR strains ameliorated tomato emergence, shoot growth and chlorophyll content under lower levels of salt stress. However, PGPR have little or no effect on tomato root growth under salt stress. Moreover, induction of tomato salt stress tolerance by PGPR is strain-specific. Application of PGPR to enhance stress tolerance in plants is a feasible strategy for improving crop production in saline environments. The effect of PGPR on tomato growth, yield, and fruit quality was conducted under field stresses in northeast Alabama. Commercially available PGPR products can lessen the stress of transplant shock and nitrogen stress resulting from organic fertilizer. PGPR treatments consistently resulted in significantly higher plant growth indices compared to nonbacterized control. With organic fertilizer, tomato fruits had significantly higher sugar and vitamin C contents compared to tomato fruits grown with inorganic fertilizer. Although marketable yield was less with organic fertilizer, fruit quality was higher. Moreover, some PGPR products in combination with organic fertilizer contributed to the improvement of tomato flavor quality and nutrient quality.